1. Technical Field of the Invention
This invention relates generally to wireless communications systems and more particularly to wireless communication devices.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
Even though wireless communication devices include a transmitter and receiver, they generally communicate in a half duplex manner, i.e. they are either transmitting or receiving. As such, a wireless communication device may include a single antenna structure, which may include one antenna or a diversity antenna structure that is shared by the receiver and the transmitter of the device. To facilitate the sharing of the antenna structure, the wireless communication device includes at least one transmit/receive (T/R) switch.
In general the T/R switch couples either the receiver path or the transmitter path of the wireless communication device to the antenna structure. Since the T/R switch is coupling radio frequency (RF) signals in the megahertz to gigahertz range, the T/R switch must have a stable frequency response over the frequency range of interest. As such, the T/R switch is generally an off chip device or is fabricated using gallium arsenide integrated circuit process. Neither implementation is ideal for a CMOS implemented radio frequency integrated circuit (RFIC).
Another issue with T/R switches is when used by a wireless communication device that employs a diversity antenna structure. As is known, a diversity antenna structure includes two or more antennas that are physically separated (e.g. by a quarter wave length, half wave length, or full wave length) but receive the same signal. The antenna that receives the signal with the largest signal strength is selected for use by the wireless communication device. For a two antenna diversity structure, the wireless communication device includes two transmit receive switches: one to select the transmit or receive path and the other to select the first or second antenna. In this instance, since the RF signals are traversing two T/R switches, the T/R switches need to be extra clean (i.e. have a flat frequency response over the frequency range of interest and induce very little noise) making it essential to use off chip T/R switches or gallium arsenide integrated circuit T/R switches in conjunction with a CMOS radio frequency integrated circuit, which dramatically adds to the cost of a radio frequency integrated circuit.
Therefore, a need exists for an on chip implementation of a transmit receive switch that provides clean RF switching for single or diversity antenna structures.